This invention relates to the preparation and purification of dialkylamino metal compounds.
As used herein, the terms xe2x80x9cdihydrocarbylamino metal compoundxe2x80x9d and xe2x80x9cdihydrocarbylamido metal compoundxe2x80x9d are synonymous. Such compounds are also referred to as metal amides. Also, as used herein, the term xe2x80x9chalometal amidexe2x80x9d means a metal compound that contains both halide and dihydrocarbylamino ligands.
Metal amides, particularly homoleptic dialkylamino metal compounds, are useful as precursor compounds for chemical vapor deposition. See in this connection U.S. Pat. Nos. 5,178,911; 5,417,823; and 6,080,446. Such metal amides are also useful in the synthesis of polymerization catalysts; see for example U.S. Pat. No. 6,020,444. The usual method employed for making metal amides is to react a metal halide with lithium amide, and to purify the product via vacuum distillation. See D. C. Bradley and I. M. Thomas, Proc. Chem. Soc., 1959 225-226, D. C. Bradley and I. M. Thomas, J. Chem. Soc., 1960 3857-3861; and M. T. Reetz et al., Synthesis, 1983 7 540. Most often, the lithium amide is made from butyl lithium or lithium, expensive reagents, and the corresponding amine. When a lithium amide is used, the solid lithium halide by-product often consists of very small particles that are difficult to remove, especially at large scales. An alternative method employs halomagnesium amide in place of lithium amide; see D. Steinborn et al., Synthesis, 1989 4 304, and DD 269387 A1. After either synthetic procedure, the metal amide is usually purified by vacuum distillation. Many metal amides decompose at the distillation temperature, causing yield losses.
Also known in the art are metal complexes having both halide and dialkylamino ligands. Such compounds can be made by ligand exchange between, for example, TiCl4 and Ti[N(CH3)2]4, or by the use of less than four moles of LiN(CH3)2 when the reactant is TiCl4, see U.S. Pat. No. 3,370,041. Another approach, described by R. T. Cowdell and G. W. A. Fowles, J. Chem. Soc., 1960 2522-2526, is reacting TiCl4 with four moles of dialkylamine, which results in the replacement of only one chlorine ligand. The halide ligands on these halometal amide compounds have been replaced with organic groups; for example, TiBr[N(CH3)2]3 is reacted with methyllithium; see H. Burger and H. J. Neese, J. Organometallic Chem., 1969 20 129-139.
It has been reported that reaction occurs when dialkylamino metal compounds are contacted with acetonitrile. See D. C. Bradley and M. C. Ganorkar, Chem. Ind., 1968 1521-1522, and D. C. Bradley and M. Ahmed, Polyhedron, 1983 2 87. The reaction of TiCl4 with acetonitrile in the presence of amines has been described by N. A. Chumaevskii et al., Koord. Khim., 1991 17 463-466 (Chemical Abstracts, 115:84101n, 1991).
It would be advantageous to find a better synthetic route to dialkylamino metal compounds. A more effective purification method for these compounds is also desirable.
This invention is deemed to enable achievement of the above advantages.
The process of this invention for making the dihydrocarbylamino metal compound has the advantage that the amount of alkali metal amide used decreases from four moles to less than about two moles, and the amount of alkali metal halide by-product produced is correspondingly reduced. Additionally, the dihydrocarbylamino metal compound does not have to be purified via distillation.
An embodiment of this invention is a process of preparing dihydrocarbylamido metal compounds. This process comprises bringing together, in a liquid reaction medium, at least one metal halide, MX4, where M is titanium, zirconium, or hafnium, and X is a halogen atom, with at least one dihydrocarbylamine, such that a mixture of (i) halometal amides in which the atom ratio of halogen to metal is greater than about 0.1 and less than about 2, and (ii) dihydrocarbylamine hydrohalide is produced. Then (i) and (ii) are separated from each other, and (i) is brought together with an alkali metal amide, ANR2, where A is an alkali metal, and R is a hydrocarbyl group, in a liquid medium, to produce a product comprised of substantially halogen-free dihydrocarbylamido metal compound.
Another embodiment of this invention is also a process of preparing dihydrocarbylamido metal compounds. This process comprises reacting at least one alkali metal dihydrocarbylamide, ANR2, where A is an alkali metal, and R is an hydrocarbyl group, with at least one halometal amide in which the atom ratio of halogen to metal is greater than about 0.1 and less than about 2, where the metal of the halometal amide is titanium, zirconium, or hafnium, to produce a product comprised of substantially halogen-free dihydrocarbylamido metal compound.
Still another embodiment of this invention is the discovery that dihydrocarbylamido metal compounds can be purified by contact with a nitrile. Thus, this purification step can be performed in connection with the other embodiments of this invention.
Other embodiments and features of this invention will become still further apparent from the ensuing description and appended claims.
The metal halides used in invention have the formula MX4, where M is titanium, zirconium, or hafnium, and X is a halogen atom. The halogen atom can be a fluorine, chlorine, bromine, or iodine atom. Normally and preferably, all four halogen atoms are the same, as such reagents are readily available commercially. Thus, suitable metal halides include titanium tetrafluoride, titanium tetrachloride, titanium tetrabromide, titanium iodide, zirconium tetrafluoride, zirconium tetrachloride, zirconium tetrabromide, zirconium iodide, hafnium tetrafluoride, hafnium tetrachloride, hafnium tetrabromide, and hafnium iodide. Preferably, the metal is titanium or zirconium, more preferred as the metal is titanium. The halogen atom is preferably a chlorine, bromine, or iodine atom, more preferably, the halogen atom is a chlorine or bromine atom. Highly preferred metal halides for use in this invention thus are titanium tetrachloride, titanium tetrabromide, zirconium tetrachloride, and zirconium tetrabromide.
Dihydrocarbylamines that can be used in this invention have hydrocarbyl groups that may be the same or different, and each hydrocarbyl group has, independently, from 1 to about 12 carbon atoms. Preferably, each hydrocarbyl group has from 1 to about 5 carbon atoms, preferred dihydrocarbylamines are those in which the hydrocarbyl groups are the same. Examples of dihydrocarbylamines that can be used include, but are not limited to, dimethylamine, dimethylamine, ethylmethylamine, ethyl-n-propylamine, methyl-n-propyl-amine, di-n-propylamine, diisopropylamine, methylisopropylamine, ethylisopropylamine, n-butylethylamine, di-n-butylamine, diisobutylamine, isobutylpropylamine, dicyclobutylamine, (cyclobutyl)(methyl)amine, dipentylamine, methylpentylamine, (n-propyl)(pentyl)amine, dicyclopentylamine, (cyclopentyl)pentylamine, dihexylamine, ethylhexylamine, dicyclohexylamine, (isopropyl)(cyclohexyl)amine, diheptylamine, dicycloheptylamine, dioctylamine, n-butyloctylamine, methyloctylamine, dicyclooctylamine, dinonylamine, ethylnonylamine, isobutyldecylamine, didecylamine, (methyl)(phenyl)amine, (ethyl)(phenyl)amine, diphenylamine, bis(biphenyl)amine, ditolylamine, dixylylamine, di(ethylphenyl)amine, di(isopropylphenyl)amine, (n-propyl)(tolyl)amine, dinaphthylamine, (cyclohexyl)(naphthyl)amine, pyrrolidine, pyrrole, and piperidine. Preferred dihydrocarbyl-amines are dimethylamine, diethylamine, and di-n-propylamine, more preferred are dimethylamine and diethylamine. Mixtures of two or more dihydrocarbylamines may be used; preferably, a single dihydrocarbylamine is used.
For the bringing together of the metal halide and the dihydrocarbylamine, the liquid reaction medium can be comprised of one or more alkanes, aromatic hydrocarbons, hydrocarbylaromatic hydrocarbons, ethers, or mixtures thereof, that are liquid at the conditions at which the addition is conducted. When the dihydrocarbylamine being used is a liquid, the process can be done in the absence of additional component(s). Suitable components of the liquid reaction medium include pentane, cyclpentane, hexane, cyclohexane, methylcyclohexane, cyclohexene, heptane, cycloheptane, octane, isooctane, cyclooctane, cyclooctadiene, nonane, benzene, toluene, xylene, diethyl ether, di-n-propyl ether, ethyl-n-propyl ether, diisopropyl ether, tert-butyl ethyl ether, di-n-butyl ether, diheptyl ether, oxetane, tetrahydrofuran, methyltetrahydrofuran, 1,4-dioxane, 1,3-dioxolane, cyclohexylmethyl ether, and the like. A preferred type of component of the liquid reaction medium are alkanes. Preferred alkanes are pentane, hexane, cyclohexane, heptane, octane, and isooctane; more preferred are hexane, cyclohexane, and heptane. The most preferred liquid reaction medium comprises hexane and/or cyclohexane.
The alkali metal amide has the formula ANR2, where A is an alkali metal, and R is an hydrocarbyl group. The alkali metal is preferably lithium, sodium, or potassium; more preferable are lithium and sodium; most preferred is lithium. The two hydrocarbyl groups of the amide may be the same or different, and are as described above for the dihydrocarbylamines. Suitable alkali metal amides include, for example, lithium dimethylamide, sodium dimethylamide, potassium dimethylamide, lithium ethylmethylamide, sodium ethylmethylamide, potassium ethylmethylamide, lithium diethylamide, sodium diethylamide, potassium diethylamide, lithium di-n-propylamide, sodium di-n-propylamide, potassium di-n-propylamide, lithium diisopropylamide, sodium ethyl-n-propylamide, potassium methylisopropylamide, lithium di-n-butylamide, sodium diisobutylamide, potassium n-butylethylamide, lithium dicyclobutylamide, sodium dipentylamide, potassium methylpentylamide, lithium dicyclopentylamide, sodium dihexylamide, potassium ethylhexylamide, lithium dicyclohexylamide, sodium dihepylamide, potassium dioctylamide, lithium methyloctylamide, sodium dicyclooctylamide, potassium dinonylamide, lithium ethylnonylamine, sodium didecylamine, potassium (methyl)(phenyl)amide, lithium (ethyl)(phenyl)amide, sodium diphenylamide, potassium ditolylamide, lithium (n-propyl)(tolyl)amide, sodium dinaphthylamide, potassium (cyclohexyl)(naphthyl)amide, lithium-pyrrolidine salt, sodium-pyrrole salt, and potassium-piperidine salt. Preferred alkali metal amides are lithium dimethylamide, sodium dimethylamide, lithium diethylamide, sodium diethylamide, lithium dipropylamide, and sodium dipropylamide. Most preferred are lithium dimethylamide and lithium diethylamide.
When it is said that the alkali metal amide corresponds to the dihydrocarbylamine, it is meant that the amide has the same two hydrocarbyl groups as the amide ligands of the halometal amide. Using an alkali metal amide that has hydrocarbyl groups which correspond to those of the halometal amide is preferred.
When there will be solvent as part of the liquid reaction medium, the amine is normally mixed with such solvent prior to being brought together with the metal halide. The metal halide may be brought together with the amine as a solid, or in a mixture with a suitable solvent. Such solvents are those described above for used as components of the liquid reaction medium. When the metal halide is in a mixture with a solvent, it is preferred that the metal halide is soluble in that solvent. Preferably, the metal halide is a solution or slurry in a suitable solvent; most preferable is to use the metal halide as a solution in a suitable solvent. It is also preferred that some liquid is present when the process is finished to prevent the slurry from becoming too viscous to transfer easily.
Without wishing to be bound by theory, it is believed that the metal halide must be in the presence of a locally high concentration of dihydrocarbylamine for the process to be successful. When the metal halide is present in higher concentration relative to the amine, trihalometal amide products and/or tars are usually produced. Mixing during the bringing together of the metal halide and the dihydrocarbylamine is important to avoid locally high concentrations of metal halide (and thus locally low concentrations of amine). Generally, stirring of the reaction mixture both during and after the bringing together of the metal halide and the dihydrocarbylamine is vigorous. If the reaction mixture is not stirred after the bringing together, it usually becomes a very viscous slurry which is not easy to transfer. Typical methods of bringing the amine and metal halide together include cofeeding (where the feed of amine is such that a locally high concentration of amine is present relative to the metal halide) and addition of the metal halide to a vessel containing the dihydrocarbylamine.
At least about a slight molar excess of dihydrocarbylamine relative to metal halide preferably is used in the process. An equimolar amount is about one mole of dihydrocarbylamine for each mole of halide ligands; thus, four moles of dihydrocarbylamine for each mole of MX4 is considered to be the equimolar amount.
During the bringing together of the metal halide and the dihydrocarbylamine, the reaction temperature is preferably kept low, cooling is often necessary to maintain the low temperature because the reaction is exothermic. Preferably, the temperatures are no higher than about 40xc2x0 C., more preferably, the temperature is no higher than about 20xc2x0 C. The temperature is most preferably no higher than about 5xc2x0 C. Allowing the temperature to rise above about 60xc2x0 C. is believed to decrease the yield of the desired product by increasing the rate of the side reactions.
In the practice of this invention, the halometal amides produced have an atom ratio of halogen to metal greater than about 0.1 and less than about 2. The process typically produces mixtures of monohalometal amides and dihalometal amides, with a varying ratio of monohalometal amide to dihalometal amide. The atom ratio becomes lower as more monohalometal amide is produced relative to dihalometal amide. When the halometal amide is made as an intermediate compound before making a dihydrocarbylamido metal compound, the process is preferably optimized to produce halometal amides with lower atom ratios of halogen to metal. This minimizes the amount of alkali metal amide needed to make the dihydrocarbylamido metal compound.
Halometal amides having an atom ratio of halogen to metal greater than about 0.1 and less than about 2, however made, may be brought together with alkali metal amides to produce a substantially halogen-free dihydrocarbylamido metal compound. By using the phrase xe2x80x9csubstantially halogen-free,xe2x80x9d it is recognized that the dihydrocarbylamido metal compound, which is desirably halogen-free, may contain small amounts of adventitious halogen.
Normally, the halometal amide and alkali metal amide are brought together in a liquid medium in which the alkali metal amide is soluble, although it is not necessary for the alkali metal amide to be dissolved for the process to work. It is preferred to use a liquid medium in which the alkali metal amide is soluble. The halometal amide may be in the form of a solvent-free liquid, a slurry, or a solution when it is brought together with the alkali metal amide. When the halometal amide is a liquid, it need not be mixed with another component to form a solution before being brought together with the alkali metal amide. This process is preferably performed at temperatures in the range of about xe2x88x9215xc2x0 C. to about 40xc2x0 C., to keep the temperature in this range usually requires cooling because the reaction is exothermic. Preferably, the temperature is in the range of about 0xc2x0 C. to about 20xc2x0 C. Stirring during the bringing together of the halometal amide with the alkali metal amide is typically vigorous.
Means for solubilizing alkali metal amides generally involve including a Lewis base in the liquid medium. Such Lewis base may be added before, during, and/or after the halometal amide and the alkali metal amide are brought together. Acceptable Lewis bases are those that solubilize the alkali metal amide and do not adversely affect the process, e.g., by reacting with the halometal amide. Mixtures of Lewis bases may be employed, but use of a single Lewis base is preferred. Suitable types of Lewis bases include, for example, trialkylamines and ethers. Trialkylamines that can be used include trimethylamine, ethyldimethylamine, triethylamine, tri-n-propylamine, triisopropylamine, tri-n-butylamine, tricyclohexylamine, and the like. A preferred trialkylamine is triethylamine. Suitable ethers include diethyl ether, di-n-propyl ether, ethyl-n-propyl ether, diisopropyl ether, tert-butyl ethyl ether, di-n-butyl ether, diheptyl ether, oxetane, tetrahydrofuran, methyltetrahydrofuran, cyclohexylmethyl ether, and the like. Preferred ethers are diethyl ether, tetrahydrofuran, and methyltetrahydrofuran. Ethers are a preferred type of Lewis base. The use of enough Lewis base to dissolve the alkali metal amide is preferred, a greater amount of Lewis base is not expected to harm the process. For an ether, it is preferred to have at least about one mole of ether per mole of alkali metal cation present in the liquid medium.
It has been discovered that dihydrocarbylamido metal compounds can be purified by contact with a nitrile. Usually, the mixture undergoing treatment contains mostly metal amide, alkali metal halide, and unreacted alkali metal amide. For the nitrile treatment, at least enough nitrile to consume leftover alkali metal amide should be used. Preferably, an excess amount of nitrile is used, because, without wishing to be bound by theory, it is thought that the nitrile also consumes other undesired side products, such as reduced metal species.
The dihydrocarbylamido metal compound can be purified by contact with a nitrile in a number of ways. One preferred manner in which to carry out the nitrile treatment is to perform several nitrile washes of the metal amide product. For these washing procedures, the temperature at which the nitrile treatment is conducted is preferably in the range of about xe2x88x9230xc2x0 C. to about 40xc2x0 C. to minimize undesired side reactions, which usually include decomposition of the dihydrocarbylamido metal compound. More preferably, the temperature is in the range of about xe2x88x9230xc2x0 C. to about 25xc2x0 C., most preferred is a temperature in the range of about xe2x88x9215xc2x0 C. to about 0xc2x0 C. Contact times are normally less than about 36 hours, preferably less than about 6 hours, and most preferably in the range of about 1 to 4 hours on the laboratory scale. Good results at room temperature may be obtained by decreasing the contact time of the nitrile and the dihydrocarbylamino metal compound. However, improved removal of the alkali metal species has been observed at lower temperatures.
Suitable nitriles include acetonitrile, acrylonitrile, propionitrile, glutaronitrile, cyclopropyl cyanide, butyronitrile, isobutyronitrile, 1,4-dicyanobutane, 3-butenonitrile, valeronitrile, 1,5-dicyanopentane, 1,6-dicyanohexane, cyclohexyl cyanide, cycloheptyl cyanide, n-heptyl cyanide, undecyl cyanide, benzonitrile, trimethylbenzonitrile, trimethylacetonitrile, diphenylacetonitrile, diphenylpropionitrile, tolunitrile, dicyanobenzene, benzyl cyanide, methylbenzyl cyanide, cinnamonitrile, poly(acetonitrile), poly(propionitrile), poly(butyronitrile), and polyacrylonitrile. Preferred nitriles are acetonitrile, propionitrile, butyronitrile, and poly(acetonitrile), poly(propionitrile), and poly(butyronitrile), more preferred are acetonitrile, propionitrile, and butyronitrile. The most preferred nitrile in the practice of this invention is acetonitrile.
There are no particular requirements for the result of the nitrile treatment, except that it should render the dihydrocarbylamino metal compound separable from the nitrile-derived products, preferably, the dihydrocarbylamino metal compound is rendered separable from both the nitrile-derived products and other impurities. Upon treatment with nitrile, the impurities typically form solid products which can be separated from a liquid dihydrocarbylamino metal compound or a solution of a dihydrocarbylamino metal compound via filtration. When filtration is not desirable and/or feasible, it may be possible to separate the nitrile-derived products and other impurities from the dihydrocarbylamino metal compound by centrifugation or by selective absorption of either the dihydrocarbylamino metal compound or its impurities on a solid material such as silica, alumina, titania, or montmorillonite.